As water-base curable resin compositions for coating materials, a water-base curable resin composition has been hitherto widely used which comprises a water-base resin and one of various curing agents such as an epoxy resin, an isocyanate resin, and an amino resin. The water-base resin mentioned above can be obtained by neutralizing a vinyl polymer, having a basic or acid group together with a functional group such as a hydroxyl group, with an acidic or basic compound, and thereafter dispersing or dissolving the resulting neutralized vinyl polymer in a water-base medium (Japanese Patent Application, First Publication (Kokai) No. Hei 4-359075, Japanese Patent Application, First Publication (Kokai) No. Hei 6-1948, Published Japanese Translation of PCT International Publication (Kohyo) for Patent Application, Publication No. Hei 8-510000, and European Patent Application, Publication No. EP661320-A1).
However, cured coating films obtained from such water-base curable resin compositions which have hitherto been used in which a water-base resin serves as a base resin component are insufficient in durability during outdoor exposure such as gloss retention and acid rain resistance, or in stain resistance during outdoor exposure. Accordingly, there have been problems in that conventional water-base resins can almost never be put into uses where high durability or stain resistance during outdoor exposure is demanded.
On the other hand, in order to improve gloss retention during outdoor exposure of the coating film which is obtained from the water-base vinyl polymer as described above, modifications of the polymer by polysiloxanes have been investigated. However, at present, a modified resin having a high polysiloxane content which is excellent in both storage stability and curability at room temperature has not yet been obtained.
Thus, the present inventors commenced study in order to solve all of these various problems which existed in the prior art as described above.
Accordingly, the object to be achieved by the present invention is to provide a novel and useful process for producing a water-base resin which possesses both excellent storage stability and excellent curability at room temperature, and which can produce a cured material having excellent durability such as gloss retention and acid rain resistance during outdoor exposure, and exhibiting extremely excellent stain resistance during outdoor exposure. Another object to be achieved by the present invention is to provide a novel and useful water-base curable resin composition which comprises the novel and useful water-base resin obtained by the above production process. The water-base curable resin composition is excellent in curability at room temperature and is capable of producing a cured coating film which possesses extremely excellent durability.
Yet another object to be achieved by the present invention is to provide a process for forming a coating film in which a coating material comprising the above water-base curable resin composition is used.